Environmental isotopic study for groundwater of the North Plain of Huai He River, China

The Huai He River, one of the seven main rivers in China, has a drainage area of 164,000 km2 until Hongze Lake. The North Plain of Huai He River (NPH) covers an area of approximately 85,000 km2. Due to the complex alluvial and diluvial depositional cycles, the aquifers are layered, discontinued, connected and, leaked. From hydrogeological settings and their isotopic features, shallow and deep groundwater are defined, the boundary of Lower and Middle Pleistocene is taken as the general boundary of them. Shallow groundwater is phreatic and/or slight confined while the deep groundwater is confined. The river water line of δD and δ18O is close to that of the groundwater with depths of 0-30 m. The low flow of rivers is not only recharged from the Holocene deposit/aquifers but that of the Upper Pleistocene. From the original composition of the shallow groundwater and the monthly mean composition of precipitation, it is found that the shallow groundwater is sourced from local precipitation and aquifers of the Upper Pleistocene. Three recharge sources of deep groundwater are identified from uranium disequilibrium, the mixing diagram of uranium content U and 234U/238U, also from that of 18O versus 234U excess, they are: the metrological water from modern precipitation, the phreatic shallow groundwater and, the palaeowater. The recharge from the percolation of perched Yellow River situated to the north boundary of NPH to the deep groundwater is demonstrated by the profile of δ18O, the existence of tritium in groundwater even from the borehole with depth of 1300 m. The recharge extends about 150 km from the Yellow River. (author)